Microstructure Damage Evolution and Life Prediction of Dissimilar Nickel-Based High-Temperature Alloy Welded Joints under Cyclic Loading

Dissimilar welding of nickel-based high-temperature alloys is essential for aerospace and power components, yet fatigue performance is often limited by fusion-boundary incompatibilities, brittle secondary phases, and tensile residual stresses. Here, we present an integrated experimental-computational framework for a laser-arc hybrid butt weld joining two precipitation-hardened Ni-based alloys using an engineered Ni-based interlayer. High-resolution EBSD/KAM mapping identifies narrow, high-misorientation fusion-boundary bands as the dominant strain-localization zones, consistent with observed crack initiation sites. Residual stresses measured by X-ray diffraction and contour-method mapping reveal pronounced longitudinal tensile peaks near the fusion boundaries (≈500 MPa), which are accurately reproduced by a calibrated thermo-mechanical finite-element weld simulation. High-cycle and strain-life fatigue tests at room temperature and 550 °C confirm significant weld softening and reduced fatigue strength relative to both base alloys, while fractography and EBSD crack-path analysis link early damage to brittle fusion-boundary networks and residual-stress hotspots. A unified finite-element life model incorporating local hardness, KAM, and measured σ_L within a Smith-Watson-Topper damage parameter predicts fatigue life across base and welded regions with high accuracy (R² ≈ 0.97). Finally, DOE/response-surface optimization identifies a safe-life plateau and a Pareto-optimal parameter condition that increases fatigue life while constraining cycle time. The Ni-based interlayer further improves life in the critical fusion-boundary/HAZ region by approximately threefold and enables an ≈7× B10 reliability gain, supporting fewer inspections over a 10-year service window.